The entire disclosure of Japanese Patent Applications No. Hei 11-296636 filed on Oct. 19, 1999 and No. 2000-309235 filed on Oct. 10, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a cryogenic refrigerating device, and more particularly to a cryogenic refrigerating device having an adiabatic vacuum tank and a refrigerator accommodated in the adiabatic vacuum tank.
2. Description of Related Art
It is necessary for an electronic device to be refrigerated to a temperature level of liquefied nitrogen (about 80K) in order to maintain or to generate a particular characteristic thereof. This type of cryogenic refrigeration is often achieved by a refrigerator such as GM (Gifford-McMahon) type refrigerator or pulse tube refrigerator for cooling the electronic device. In order to minimize the effect of external heat, such refrigeration is carried out in an adiabatic vacuum tank. Therefore, such a refrigerating device generally includes an adiabatic vacuum tank and a refrigerator disposed in the tank.
The conventional refrigerating device, however, has a drawback in that the pressure in the adiabatic vacuum tank increases due to molecules released from the metal inner surface of the tank or molecules adhered on the inner wall of the tank and released therefrom. This pressure increase in the tank has been prevented by various means hitherto proposed. One such proposal is to provide a vacuum pump within the adiabatic vacuum tank. According to this proposal, the molecules generated and released in the tank are discharged by the vacuum pump.
Another proposal is to provide a panel (adsorption panel) to which is attached a porous material, such as activated carbon, in the cold head portion (low temperature generating portion) of the refrigerator accommodated in the adiabatic vacuum tank. According to this proposal, molecules floating in the cold head portion of the refrigerator are adsorbed and trapped in the panel. This will prevent an increase of the pressure in the tank.
A further proposal is to provide a hydrogen storage alloy (for example, vanadium alloy) in the adiabatic vacuum tank. According to this proposal, the hydrogen molecules are stored in the hydrogen storage alloy, and other molecules having a relatively high freezing point (for example oxygen molecules) are chemically reacted with the hydrogen storage alloy to generate a chemical compound such as oxide (vanadium oxide), and so are kept in the alloy.
These proposals, however, have certain drawbacks. According to the first proposal of providing a vacuum pump in the adiabatic vacuum tank, the vacuum level in the tank is limited to the capacity of the vacuum pump. In order to obtain a desired high vacuum level in the tank, the vacuum pump has to be large and expensive. This leads to high cost and a larger size refrigerating device as a whole. Further, it is necessary to provide an additional driving source and device for driving the vacuum pump in addition to the driving of the refrigerator itself. The consumption of energy becomes large and the refrigeration system cannot maintain the vacuum within the system independent of the vacuum pump.
According to the second proposal of providing an adsorption panel, while it needs no vacuum pump, the adsorption panel cannot trap molecules such as hydrogen molecules having a freezing point below the ambient temperature of liquefied nitrogen level (about 80K). The vacuum level may therefore increase over time due to the release of hydrogen molecules from the tank inner wall. This problem may be addressed by improving the performance capacity of the refrigerator to lower the temperature at the cold head to about 20K so that even the hydrogen molecules may be trapped in the panel. It is, however, not realistic to improve the capacity of refrigerator just for the purpose of trapping the molecules, because the basic role of the refrigerator is to cool the electronic devices to be refrigerated and not to trap gas molecules. Also, excess cooling or refrigeration may reduce the performance of the electronic devices to be cooled.
According to the third proposal of providing the hydrogen storage alloy, it can store the hydrogen molecules in the alloy and at the same time keep the other molecules of higher freezing point in the alloy as chemical components by chemical reaction with the alloy. However, the amount of other molecules of higher freezing point to be kept in the alloy is very small compared to the hydrogen molecules and accordingly the hydrogen storage alloy has to be re-activated by being heated to 500 to 800xc2x0 C. This heating requires a heating device, which leads to an increase in consumption of electric power. Further, during the operation of the refrigerating device, such reactivation has to be done frequently.
As stated, the conventional proposals are unable to provide an inexpensive cryogenic refrigerating device having an adiabatic vacuum tank, or such a tank capable of long time stable operation to keep the vacuum at a constant level.
It is therefore, an object of the present invention to provide an improved cryogenic refrigerating device which can obviate the above conventional drawbacks.
It is another object of the present invention to provide an improved cryogenic refrigerating device having an adiabatic vacuum tank and a refrigerator, a part thereof formed integrally with the adiabatic vacuum tank, without increasing the cost, and yet capable of keeping the vacuum level in the adiabatic vacuum tank to a desired and stable level for a relatively longer time or for a lifetime of operation.
According to the present invention, a cryogenic refrigerating device includes an adiabatic vacuum tank, a refrigerator having at least a low temperature generating portion (a cold head portion) thereof being disposed in the adiabatic vacuum tank, an adsorption panel attached to the low temperature generating portion of the refrigerator, and a hydrogen sorbing device provided in the adiabatic vacuum tank for sorbing the hydrogen molecules therein.
According to the present invention, the adsorption panel attached to the low temperature generating portion of the refrigerator adsorbs molecules other than the hydrogen in the adiabatic vacuum tank, and a hydrogen sorbing device provided in the adiabatic vacuum tank sorbs the hydrogen molecules selectively. The adsorption panel adsorbs molecules of relatively high freezing point in the adiabatic vacuum tank and the hydrogen sorbing device sorbs hydrogen molecules of lower freezing point in the adiabatic vacuum tank selectively, so that most of the molecules in the adiabatic vacuum tank may be trapped either in the adsorption panel or in the hydrogen sorbing device.
The adsorption panel may include an activated carbon layer or molecular sieve for adsorbing the relatively high freezing point molecules in the adiabatic vacuum tank. The hydrogen sorbing device is formed for sorbing molecules of lower freezing point such as hydrogen and may include hydrogen storage alloys such as vanadium alloy or zirconium alloy.
During the operation of the cryogenic refrigerating device, relatively high freezing point molecules such as oxygen or nitrogen are adsorbed by the adsorption panel provided on the low temperature generating portion of the refrigerator and relatively low freezing molecules such as hydrogen are adsorbed by the hydrogen sorbing device provided in the adiabatic vacuum tank. Accordingly, the hydrogen molecules in the adiabatic vacuum tank are sorbed by the hydrogen sorbing device and the molecules other than hydrogen are adsorbed by the adsorption panel, to thereby sorb most of the molecules generated or present in the adiabatic vacuum tank during operation, thereby to keep the vacuum level in the tank to a desired level for a long time.
This structure does not include a vacuum pump and yet keeps the vacuum level in the tank constant by use of the cryogenic refrigerating device itself, without using an external driving device. This structure is advantageous in cost and in size.
The molecules which cannot be adsorbed by the adsorption panel can be sorbed by the hydrogen storage material. This will keep the vacuum level in the adiabatic vacuum tank constant for long time without increasing the pressure in the tank due to the generation of the hydrogen or other molecules.
This structure is further advantageous because the hydrogen molecules are sorbed by a hydrogen sorbing device, and molecules other than hydrogen are adsorbed by a different adsorbing means (adsorption panel). This does not generate chemical components due to the chemical reaction of the hydrogen with other molecules. Accordingly, it is not necessary to reactivate the hydrogen sorbing device, which accordingly needs no extra devices such as a heating device for reactivation. The working efficiency is also improved by not reactivating the hydrogen adsorbing device during the operation.
The molecules in the adiabatic vacuum tank are molecules remaining in the vacuum in the tank, molecules released from the inner wall of the tank, and molecules once stored in the inner wall of the tank and then released. Molecules remaining in the vacuum tank are mainly nitrogen N2 and oxide O2, molecules released from the inner wall of the tank are mainly H2O, and molecules stored in the inner wall and then released are mainly H2.
According to another aspect of the present invention, in addition to the structure above, the hydrogen adsorbing device is a hydrogen storage alloy. The hydrogen storage alloy includes a relatively large amount of hydrogen solid solution for hydrogen sorbing, and it is not necessary to change the alloy due to the saturation of the hydrogen solid solution for the lifetime of the refrigerating device. This will reduce the running cost of the device.
According to a further aspect of the present invention, the refrigerator is connected to an uninterruptible power source. Since the refrigerator is connected to the uninterruptible power source, should the power fail, the refrigerating device can continue in its operation. If the refrigerating system were to stop suddenly, the low temperature generating portion (cold head portion) would not be cooled and the adsorbed molecules in the panel may again be released in the adiabatic vacuum tank. When the power is supplied again to operate the refrigerating device, the vacuum level in the adiabatic vacuum tank would already have been reduced and the heat insulating function would be poor, which may lead to heat invasion into the tank. Thus the cold head portion could not generate the low temperature necessary not to again adsorb the molecules once released in the vacuum. The refrigerator accordingly could not function sufficiently to comply with the required refrigeration performance.
In the structure above, the refrigerator is connected to an uninterruptible power source to continue the refrigeration operation even when the power supply stops for a predetermined period. During this time, the device can be connected to an emergency power generating system.
As to the adsorption panel, any panel may be used as long as molecules other than hydrogen can be adsorbed. It is preferable to use a panel made of good heat conductive material and connected to the low temperature generating portion of the refrigerator. The panel may include activated carbon or a molecular sieve attached to the panel.
As to the hydrogen storage alloy, any alloy may be used as long as the hydrogen molecules can be sorbed and stored. It is preferable to use vanadium alloy or zirconium alloy.
According to a further aspect of the invention, the cryogenic refrigerating device includes an adiabatic vacuum tank, a low temperature generating portion (a cold head portion) of a refrigerator being disposed in the adiabatic vacuum tank, an adsorption panel attached to the low temperature generating portion of the refrigerator for adsorbing molecules floating in the vacuum in the adiabatic vacuum tank, and a selectively sorbing device provided in the adiabatic vacuum tank for selectively sorbing particular molecules.
According to the structure above, the particular molecules, e.g., hydrogen molecules, cannot be adsorbed by the adsorption panel, and the sorbing device may be a hydrogen storage alloy. According to the structure above, the refrigerator is connected to an uninterruptible power source.
Since the cryogenic refrigerating device includes at least a low temperature generating portion (a cold head portion) of a refrigerator disposed in the adiabatic vacuum tank, an adsorption panel attached to the low temperature generating portion of the refrigerator for adsorbing molecules floating in the vacuum in the adiabatic vacuum tank, and a selectively sorbing device provided in the adiabatic vacuum tank for selectively sorbing particular or selected molecules such as hydrogen which could not be adsorbed by the adsorption panel, the molecules in the adiabatic vacuum tank are sorbed by either the panel or by the sorbing means for keeping the vacuum pressure level in the tank constant for a long period of time.
According to a further aspect of the invention, the cryogenic refrigerating device includes an adiabatic vacuum tank, a low temperature generating portion (a cold head portion) of a refrigerator disposed in the adiabatic vacuum tank, an adsorption panel attached to the low temperature generating portion of the refrigerator for adsorbing molecules floating in the vacuum in the adiabatic vacuum tank and having high freezing point, and a selectively sorbing device provided in the adiabatic vacuum tank for selectively sorbing particular molecules floating in the adiabatic vacuum tank, in which the particular molecules sorbed by the selectively sorbing device have a freezing point lower than the freezing point of the molecules adsorbed by the adsorption panel.
According to the structure above, the particular molecules are hydrogen molecules, and the adsorbing device is a hydrogen storage alloy. According to the structure above, the refrigerator is connected to an uninterruptible power source.
Since cryogenic refrigerating device includes an adiabatic vacuum tank, a low temperature generating portion (a cold head portion) of a refrigerator disposed in the adiabatic vacuum tank, an adsorption panel attached to the low temperature generating portion of the refrigerator for adsorbing molecules floating in the vacuum in the adiabatic vacuum tank and having high freezing point, and a selectively sorbing device provided in the adiabatic vacuum tank for selectively sorbing particular molecules such as hydrogen which have a freezing point lower than the freezing point of the molecule adsorbed by the adsorption panel, the molecules in the adiabatic vacuum tank are sorbed by either the panel or by the sorbing device for keeping the vacuum pressure level in the tank constant for a long period of time.